An electrostatic microrelay known in the art is shown in FIG. 11A and FIG. 11B (Japanese Patent Laid-Open Publication HEI5-2976 and U.S. Pat. No. 5,278,368).
In this electrostatic microrelay, a moveable substrate 202 is elastically supported by a frame-like support portion 201 provided on the surface of a fixed substrate 200 so that a fixed electrode 203 formed on the upper surface of the fixed substrate 200 and a moveable electrode 204 formed on the lower surface of the moveable substrate 202 are placed facing each other. By applying a voltage between the fixed electrode 203 and the movable electrode 204, electrostatic attraction force is generated to attract the moveable electrode 204 toward the fixed electrode 203. As a result, the moveable substrate 202 is bent such that a moveable terminal 205 contacts a fixed terminal 206 to close the relay.
However, when the relay is closed at the terminals, cohesion or adhesion may occur. Therefore, in order to reliably break the contact of the terminals, elastic recovery force of the moveable substrate needs to be set large enough to separate the moveable terminal from the fixed terminal. For this reason, it is necessary to increase electrostatic attraction force between the electrodes, by, for example, increasing the driving voltage (voltage applied between the electrodes), increasing the electrode area where the electrodes are facing to each other, decreasing the distance between the electrodes, or using an electret. As a result, the volume of the microrelay has been increased and electric voltage durability of the terminals has been deteriorated, and structure and machining process of the microrelay becomes more complicated, resulting in increase of production cost.
Therefore, it is an object of the present invention to provide a microrelay having a better capability of breaking the contact of the terminals using a simple and small structure, and which can be easily manufactured at low-cost.
In order to achieve the above object, the present invention provides an electrostatic microrelay which comprises a fixed substrate having a fixed electrode thereon, and a moveable substrate having a moveable electrode thereon. The moveable substrate is positioned a selected distance from the fixed substrate. The moveable substrate faces the fixed substrate and is supported by a support member, wherein application of voltage between the moveable substrate and the fixed substrate generates an electrostatic attraction force therebetween so as to move the moveable electrode toward the fixed substrate so that a moveable terminal formed on the moveable substrate contacts a fixed terminal formed on the fixed substrate to close the microrelay. The electrostatic microrelay comprises a protrusion provided on at least one of the fixed substrate and the moveable substrate wherein the protrusion provided on one of the substrates contacts the other substrate after the movement of the moveable substrate toward the fixed substrate but before the terminals are closed.
Under this configuration, when a voltage is applied between the electrodes to generate electrostatic attraction force therebetween, a portion of the moveable substrate extending from the support member thereof is elastically deformed and the protrusion provided on either one of the substrates contacts the other substrate. By this movement, the moveable electrode comes close to the fixed electrode, thereby increasing the electrostatic attraction force. As a result the moveable substrate is partially elastically deformed around the protrusion, and the moveable electrode adheres to the fixed electrode such that the moveable terminals are closed at the fixed terminals. Thereafter, if the voltage applied between the electrodes is removed, the electrostatic attraction force disappears. In addition, the elastic force generated by the bend of the extending portion and the elastic force caused by the partial deformation of the protrusion at the time of contact with the substrate works as the separation force of the terminals. Once the protrusion is separated from the substrate, the moveable substrate recovers to its original opposing position portion due to the elastic force generated by the bend of the whole body.
The protrusion may be formed at least at one position between the support member and the moveable terminal.
The height of the protrusion may be the height or less at which the terminals can be closed by elastically deforming the moveable substrate at nearby the protrusion by using the electrostatic attraction force generated between the electrodes. For example, the height of the protrusion may be determined to be one third of the distance between the separated substrates. Under this configuration, the closing of the terminals is not obstructed by the existence of the protrusion.
By evenly supporting the moveable substrate via a plurality of beam members which extend from the moveable substrate, the moveable electrode may be smoothly moved both before and after the protrusion contacts the substrate.
Beam members elastically support the moveable substrate at two positions in point symmetry around the moveable terminal.
Signal lines are positioned on a single straight line on the fixed substrate.
The portion of the moveable substrate which opposes the signal line is removed, the moveable terminals are elastically supported at two positions which perpendicularly cross the straight line of the signal line but does not face the signal lines.
A pair of protrusions may be point-symmetrically formed around the moveable terminal where the protrusion first contacts either one of the substrates after the close of the terminals.
In this configuration, the terminal breaking force can be changed in two stages corresponding to the change of electrostatic attraction force regardless of the configuration which is adapted to the open-close operation of high frequency signals. Namely, in the range where the electrostatic attraction force is weak, the protrusions do not contact the opposing substrate, and the moveable substrate is easily deformed in accordance with electrostatic attraction force. Also, in the range where electrostatic attraction force is strong, the elastic force of the moveable substrate becomes large due to the contact of the protrusions with the opposing substrate. Moreover, the protrusion is formed in the position where it first contacts the opposing substrate after the terminals are closed. Therefore, because the elastic force of the moveable substrate can be changed at the most suitable position in relation to the electrostatic attraction curve, it becomes possible to improve the terminal separation characteristics.
The protrusions may be formed on either one of the substrates in the portion of the substrate that contacts the opposing substrate after the protrusion contacts the opposing substrate in order of precedence in which since change of the electric force by the side of the moveable contact can be made to meet the electrostatic attraction curve, it is enable to obtain suitable force of contact-breaking.
The protrusion may be formed of insulation material. By removing electrode from the portion where the protrusions contact, adhesion of organic materials between the protrusion and the electrode can be prevented, thereby achieving desired stable performance characteristics for a long period of time.
In addition, the electrostatic microrelay having the above configuration is suitable for opening and closing terminals used in wireless transmission apparatus and/or high frequency signal devices, such as radio devices and measuring devices.